Linear mechanical oscillator circuit element transducer



April. 8, 1958 w. T. HARRIS 2,830,204

LINEAR MECHANICAL oscILLAToR -clIRcuIT ELEMENT TRANsDucER Filed July 1, 1955 'Il im" hllhn" 'E1/af I l 1 l l A Maw .ATTORNEYJ' United States Patent I i 2,830,204' LINEAR MECHANICAL oser'lsron CIRCUIT.

Wilbur T., vIL-Iarr-is, Sonthburyonny assigner to The' Harris Transducer Corporjationr Woodbury, Gonnz, a corporation of Connecticut Y e Application.July1 1',1955;-SerllNo. 519,459i 10 claims; (CTI. 31o-9.6).

My. invention relates to circuit-element transducers'Y or filters of the variety in whichindependentY electrical.` input and output circuits may be coupled solely by'mechanical means.` invention` incorporates.- certain improve- `ments and;A mod icationsover that disclosedt inT myV coelementV transducer lending; itselt` to-,designfor response essentially at any selected frequency, out of a widerange:

It isv a` specific: object, to provider an improved' circuit element transducer which will exhibit-essentially only one characteristic resonant-frequency, determined by essen.- tially only one mechanicalfmode; of oscillationofrthe basic mechanically resonantelement thereof.

` It isanother specific: object to meet the above object-s; with avtransducer construction; lending; itself particularly to application to an intermediate-frequency range, extends ing lfrom the upper audio frequencies to substantially higher frequencies, as 'of the order of 500;-xk-cf/s` It is a general4 oject tomeet the, aboveobjects with a transducer construction which is rugged and reliable and which exhibits rlow loss Whenmeehanically coupling# two electricllcircuitst- Y i Other objects andvariousfurt-her features of novelty and invention! will be pointed out or"` will; occur toY those skilledin the var-t-f1=om-areading off the" followingf specification i-n conjunction' withA thea-accompanying drawings. In saidi drawings, whichA show, for illustrative purposes only?, preferred forms ofthe-invention:

`Figa 1 is." a simplified perspective view of a transducer or. filter` incorporati-ng featuresof the" inventiong' Figs. 2 and 3 areviewssimilar to Fig. l, but illustrating modifications;

Fig. 4 is a similar view, illustrating a multiple employment of my transducers;

Fig. 5 is a frequency-response characteristic for device of Fig. 4; and

Fig. 6 is a longitudinal sectional view of a mounted and encased transducer of my invention.

Briefly stated, my invention contemplates utilizing an elongated rod as the stabilizing element to determine coupling between an electrical input circuit and an electrical output circuit. The longitudinally resonant mode of the -rod determines the frequency at which coupling is achieved. In the forms to |be descri-bed, the rod is metal, and I prefer that a central part of 'the rod be cut away or the .recessed so as to denne a locally weakened or compliant section connecting two like end masses. The input and output electric-circuit connections are made by way of two like electromechanical `transducers bonded to opposite sides of the rod in such manner that the transducerelongation axes are aligned substantially with the longi-` tudinal axis of the rod.

2,830,204 Fateted Apri 8; 11958 Referring to- Fig. 1- of the'drawings, my invention is shown in application toy al filter or an oscillator-controltransducerelement, comprising: an elongated metal bar or rod-10` of'rectangular cross-section. Input and output electrical circuits tou the transducer are established by way ofl piezoelectric elements 11-12 which maybe bariumi titanateA slabs bondedP 'onl` opposite sides of the central region1 of the h'ar 10; For purposes of electrical connection; foil electrodes, as at 13` for the slab 12, may -be'ap'- plied'to the outer exposed surfaces of slabs 10:-11',witlrk leadf connections 14-=15- thereto.` The inner surfaces ofI the slabs may be 'bonded int Yintimate contact with the metal rod 10 so that theilatter may constitute aacommonf terminala Thus, Ilshow but a single lead' 1'6 connected to the`r rod lll, preferably,I thisfconnection is established near the center,V inasmuch;l as: longitudinal resonance will involve lea-st displacement at thef center.

The terminals -16 may constitute an input circuit, andi the terminals v14-16f may constitute an' output circuit. These circuits will be completelyv isolated, except for such' coupling. as. is: achievedv through the mechanically resonantproperties of the-bar 1'0`,` and for `the ar= rangement shown in which the elongation axes of the slabs 1'1-12 are oriented substantially parallel to` the longitudinal axis ofi the rod 10, the longitudinal-resonance frequency of the metall bar 10 substantially completely dominates the response of the transducer.

Fig'. 2 shows amodification in4 which the bar 20 is locally excavated or recessed at 21-22, the recesses21' 22 |being preferably symmetrically formed on opposite longitudinal faces ofV the rod; 20. The recesses 21-22 provide af. locally wealdenedL or compliant sectiona 2'3f tegrally interconnecting end masses 24-25, and th'epiezoelectric sla-bs 11`41`2 are` bonded' to the' bar 20. as. descri'becl-l for the caset depictedin` Fig. 1,- the. organization being; such that slabs IIL-112 are each `bonded to both end masses 24H25.

The arrangement of Fig. 3 4resembles that of Figi 2,.ex-v cept that thee recesses 212-22" areY formedV in' the same longitudinal.V faces as those to which the' slabs are: bonded. Performance of theitwoforms,` namely, theV forms `of Figs. 2 and 3, are generally similar, except that the.y =form of'Fig; 2 is' inherently morel capable of preventing llexurall modes tof vibration. On the: other'liand;Y the form of Fig. 3` combines. flexural andr longitudinal modes.

Fig.: 4' depicts a plural combinationi of my circuit-ele'- ment. transducers the1:efbein,,1,.` shown three transducers' 305-131-4321 said transducers:y 30s-3l--32 may be ofthe designa of1Figf.l 2, ands therefore of thel non-exurall. variety. Each transducer includes its own input anda output circuits, vbut all input circuits are interconnected and all output circuits are interconnected.V The resonantV properties of the transducers 30-31--32 are preferably slightly different, exhibiting responsesSlY--ST-SZ as shown in Fig. 5. By choosing the resonant frequencies f1, f2, f3, such that the Ipass bands for the elements 30-31--32 are adjacent (bandwidth being determined, for example, bythe spread between points Sdb down from peak response), it will be seen that a flat-topped bande pass lilter is realized by interconnecting the circuits as shown in Fig. 4, the connections of Fig. 4 being such as to establish all input circuits to elements 30-31--32 in parallel, and all output circuits in parallel.

The mounting of any of the described forms of my invention is readily achieved by bonding one face of any element to a block of cellular rubber or the like, as depicted at 35 in Fig. 6, for the case of the transducer element 36. For protection against dust and damage, the block 35 may, in turn, be lbonded to one inner Wall of a box or case 37 having a top panel 38, which may be bonded to the rest of the box, as by peripheral soldering, to establish a hermetically sealed device. Electrical connections to the transducer elements are made to terminal fittings 39-40, as will be understood.

It will be appreciated Vthat I have described a simple circuit-element transducer construction in which electrical performance is virtually completely dominated by longitudinal mechanically resonant properties of the elongated bar. I prefer that such 'bars be of metal so as to simplify electrical connection to the inner faces of the piezoelectric slabs. However, for other types of transducer element, it may not be necessary to employ a metal to dominate electrical performance. The mechanical mode of oscillation utilized by my transducers is such as to render the transducers particularly applicable to a range of frequencies extending from the upper audio frequency to frequencies of the order of 500 kc./s.

While I have described the invention in detail for the preferred forms shown, it will 'be understood that modifications may be made within the scope of the invention as defined in the claims which follow.

I claim:

l. A circuit-element transducer, comprising an elongated metal bar of rectangular cross-section, lsaid bar being centrally cut away to `the exclusion of the ends of the bar, thereby defining a compliant central portion connecting said ends, two piezoelectric slabs bonded to opposed longitudinally. extending faces of said bar and spanning said compliant central section, the elongation axes of said elements being oriented generally parallel with the longitudinal axis of said bar, and independent electriccircuit connections to said elements, whereby the mechanical properties of said bar are the sole determining factor for coupling circuits including said connections.

2. A transducer according to claim 1, and including a cushioning mounting element bonded to one face of said bar.

3. A transducer according to claim 2, in which said mounting element is of cellular rubber-like material.

4. A transducer according to claim 2, in which said mounting element is bonded to a face between said opposed faces.

5. A transducer according to claim 2, and including a hermetically sealed container for 4said bar and mounting element, said mounting element -being bonded to an inner surface of said container.

6. A circuit-element transducer, comprising an elongated Vbar centrally cut away to define a compliant section connecting two end masses, two piezoelectric elements bonded to said bar at opposed faces thereof, each piezoelectric element being in part 'bonded to one mass and in part bonded to the other mass, said masses being of substantially greater mass than said piezoelectric elements and independent electric-circuit connections to said elements.

7. A circuit-element transducer, comprising an integral mechanically resonant structure consisting of two longitudinally opposed similarly elongated end masses connected vby a central section of greater longitudinal cornpliance than longitudinal end portions of said structure, a first electro-mechanical transducer element bonded to 'both end masses and bridging said compliant section, and a second electromechanical transducer element bonded to both end masses and bridging said compliant section.

8. A circuit-element transducer, comprising an elongated metal rod of rectangular cross-section, two opposed longitudinal faces of said rod being symmetrically cut away at the longitudinal center of said rod to define a central compliant section connecting similar end masses for longitudinal mechanical resonance, `and two piezoelectric slabs bonded to opposed longitudinal faces of said rod and spanning said compliant connection, said rod being of substantially greater massthan said piezoelectric slabs, whereby mechanical resonance of said masses through said compliance may dominate electrical response of said piezoelectric slabs.

9. A circuit element transducer, comprising an elongated metal rod of rectangular cross-section, two opposed longitudinal faces of said rod being symmetrically cut away at the longitudinal center of said rod to define a central compliant section connecting similar end masses for longitudinal mechanical resonance, and two piezoelectric slabs bonded to the other two opposed longitudi nal faces of said rod and spanning said compliant connection.

10. A circuit-element transducer, comprising an elongated metal rod of rectangular cross-section, two opposed longitudinal faces of said rod being symmetrically cut away substantially only at the longitudinal center of said rod to define a central compliant section connecting similar end masses for longitudinal mechanical resonance, and two piezoelectric slabs bonded `to said opposed longitudinal faces of said rod and spanning said compliant connection.

References Cited in the file of this patent UNITED STATES PATENTS 1,693,806 Cady Dec. 4, 1928 1,866,267 Nicolson July 5, 1932 2,207,691 Crosby July 9, 1940 2,271,200 Mason Jan. 27, 1942 2,293,485 Baldwin Aug. 18, 1942 2,439,499 Williams Apr. 13, 1948 2,480,535 Alois Aug. 30, 1949 2,497,966 Via Feb. 2l, 1950 2,540,187 Cherry Feb. 6, 1951 2,640,165 Howatt May 26, 1953 

